If you've got Ethernet access to the site, may I suggest trying a Comtrol Devicemaster RS-232. These boxes are about 4"l x 4"w x ½"h and can be seen at
https://www.comtrol.com/products/catalog.asp?group=serialhubs. This is a serial to IP converter. Software--which creates a virtual serial port on the host end--also comes with it. I use it for a hotel chain that requires SMDR data gathering from all remote locations.
I had to break off Pin #6 from the unit to eliminate a pesky hardware flow control issue that software couldn't see to bypass. But other than that, it works great.